AB0545 THYMUS VARIANTS ON IMAGING IN PATIENTS WITH PRIMARY SJÖGREN’S SYNDROME AND POLYMYOSITIS/DERMATOMYOSITIS PATIENTS
Authors: O. Murata, K. Suzuki, T. Takeuchi
Journal: Annals of the Rheumatic Diseases (2022)

Background The thymus, a primary lymphoid organ, plays a crucial role in immune system homeostasis [1,2]. Although several studies of an association between radiographic thymus variants and serological features in systemic autoimmune diseases such as systemic scleroderma, have been reported [3-6], information in patients with other systemic autoimmune disease, especially in primary Sjögren’s syndrome (pSS) or polymyositis/dermatomyositis (PM/DM) patients, is quite limited. Objectives We investigated the association between radiographic thymus variants and clinical and immunological features in patients with pSS and PM/DM, and clarified its significance. Methods Patients with pSS and PM/DM were randomly selected from all patients who had visited our department and underwent chest CT scan between April 2009 and March 2019. Patients with thymoma or thymic cyst and those aged less than 30 years were excluded. Thymic enlargement and thymus attenuation score in axial images of CT scans were quantitatively interpreted. We defined thymic enlargement as a thickness of more than 13 mm and graded the score by a four-point scale (score 0-3) according to previous studies [7, 8]. Association with radiographic thymus variants and clinical and immunological features was statistically analyzed. Results 72 pSS and 47 PM/DM patients were enrolled. 90% and 63.8% were women and mean age was 62.7 ± 12.2 and 56.2 ± 13.7 years in pSS and PM/DM patients, respectively. Thymic enlargement was found in 16 (22.2%) and 14 (29.8%) patients with pSS and PM/DM, respectively. Thymus attenuation (score ≥ 2) was found in 11 (15.3%) and 9 (19.1%) patients with pSS and PM/DM, respectively. These findings were more frequent than in non-connective tissue diseases patients (9.1% and 9.1%, respectively). In pSS patients, radiographic thymus variants, both thymic enlargement and the thymus attenuation score, were significantly positively associated with body weight ( P &lt; 0.0073 and 0.037, respectively). Although there was no significant difference between immunological features such as titres of serum RF, the ratio of RF-positivity, SS-A antibody-positivity or SS-B antibody-positivity, and radiographic thymus variants, titres of serum RF tended to be positively associated with thymic enlargement ( P = 0.057). In PM/DM patients, thymic enlargement was significantly positively associated with titres of serum RF ( P = 0.046), and the thymus attenuation score was significantly positively associated with titres of serum IgG ( P = 0.042) and significantly negatively associated with age ( P = 0.033). There was no significant difference between the ratio of myositis specific antibody-positivity and radiographic thymus variants. Conclusion Radiographic thymus variants were frequently observed in pSS and PM/DM patients, and particularly, in case of PM/DM, may reflect an abnormal immune response involved in the pathogenesis. References [1]Gorozny JJ, et al. Trends Immunol 2001;22:251-255, [2]Seddon B, et al . Immunol Today 2000;21:94-99, [3]Truffault F, et al. Clin Rev Allergy Immunol 2017; 52:108-124, [4]Berrih-Aknin S, et al. J Autoimmun 2014;52:90-110, [5]Colaci M, et al. Rheumatology 2014;53:732-36, [6]Murata O, et al. Rheumatology 2021;60:5595-5600, [7]Ackman JB, et al. Radiology 2013;268:245-53, [8]Naidich DP, et al. Philadelphia: Lippincott-Raven 1999:57-73. Acknowledgements I have no acknowledgements to declare. Disclosure of Interests None declared